Predator Escape Research Articles

Flight performance in the altricial zebra finch: Developmental effects and reproductive consequences.

The environmental conditions animals experience during development can have sustained effects on morphology, physiology, and behavior. Exposure to elevated levels of stress hormones (glucocorticoids, GCs) during development is one such condition that can have long‐term effects on animal phenotype. Many of the phenotypic effects of GC exposure during development (developmental stress) appear negative. However, there is increasing evidence that developmental stress can induce adaptive phenotypic changes. This hypothesis can be tested by examining the effect of developmental stress on fitness‐related traits. In birds, flight performance is an ideal metric to assess the fitness consequences of developmental stress. As fledglings, mastering takeoff is crucial to avoid bodily damage and escape predation. As adults, takeoff can contribute to mating and foraging success as well as escape and, thus, can affect both reproductive success and survival. We examined the effects of developmental stress on flight performance across life‐history stages in zebra finches (Taeniopygia guttata). Specifically, we examined the effects of oral administration of corticosterone (CORT, the dominant avian glucocorticoid) during development on ground‐reaction forces and velocity during takeoff. Additionally, we tested for associations between flight performance and reproductive success in adult male zebra finches. Developmental stress had no effect on flight performance at all ages. In contrast, brood size (an unmanipulated variable) had sustained, negative effects on takeoff performance across life‐history stages with birds from small broods performing better than birds from large broods. Flight performance at 100 days posthatching predicted future reproductive success in males; the best fliers had significantly higher reproductive success. Our results demonstrate that some environmental factors experienced during development (e.g. clutch size) have stronger, more sustained effects than others (e.g. GC exposure). Additionally, our data provide the first link between flight performance and a direct measure of reproductive success.

Effect of Ocean Acidification on the Communications among Invertebrates Mediated by Plant-Produced Volatile Organic Compounds

Chemical communications among plant and animal components are fundamental elements for the functioning and the connectivity of ecosystems. In particular, wound-activated infochemicals trigger specifi c reactions of invertebrates according to evolutionary constraints, permitting them to identify prey cues, escape predators and optimize their behaviors according to specifi c life strategies

Probabilistic information transmission in a network of coupled oscillators reveals speed-accuracy trade-off in responding to threats.

Individuals in a group may obtain information from other group members about the environment, including the location of a food source or the presence of a predator. Here, we model how information spreads in a group using a susceptible-infected-removed epidemic model. We apply this model to a simulated shoal of fish using the motion dynamics of a coupled oscillator model, in order to test the biological hypothesis that polarized or aligned shoaling leads to faster and more accurate escape responses. The contributions of this study are the (i) application of a probabilistic model of epidemics to the study of collective animal behavior; (ii) testing the biological hypothesis that group cohesion improves predator escape; (iii) quantification of the effect of social cues on startle propagation; and (iv) investigation of the variation in response based on network connectivity. We find that when perfectly aligned individuals in a group are startled, there is a rapid escape by individuals that directly detect the threat, as well as by individuals responding to their neighbors. However, individuals that are not startled do not head away from the threat. In startled groups that are randomly oriented, there is a rapid, accurate response by individuals that directly detect the threat, followed by less accurate responses by individuals responding to neighbor cues. Over the simulation duration, however, even unstartled individuals head away from the threat. This study illustrates a potential speed-accuracy trade-off in the startle response of animal groups, in agreement with several previous experimental studies. Additionally, the model can be applied to a variety of group decision-making processes, including those involving higher-dimensional motion.

POSTURAL BEHAVIOR OF THE SEMIAQUATIC NECTOMYS (RODENTIA, SIGMODONTINAE) IN SWIMMING BOUND

Oryzomyine rodents of Nectomys have a repertoire of swimming postural behaviors used in different ecological aspects of its life, affecting key tasks of their survival. These species present three swimming behaviors: bipedal surface swimming, quadruped symmetric submerged swimming, and swimming bound, with correspondent differences in performance. Here we describe and measure the postural behavior in the swimming bound of Nectomys squamipes and N. rattus . Rodents were filmed at 30 frames s -1 in lateral view, swimming in a glass aquarium. Video sequences were analyzed dividing the swimming cycle into power and recovery phases. The two species did not differ in swimming behavior. Both species presented displacement of the head at vertical axis during impulsion, reaching its maximum displacement at the end of the phase. The power phase of the hindlimbs was primarily responsible for the animal propulsion. The flexion and extension of the head relative to the neck occurred in the impulsion and the recovery phase, respectively. During the hindlimbs power phase occurred the extension of the spine, raising the body of the animal above the water surface. The swimming bound allows a burst of speed and likely escape predation, hence involving specific postural behavior described here for the first time. These specific behaviors are related to morphological adaptations of spine, hindlimbs and feet, that allow spine extension and hindlimb thrust in an aquatic environment beyond the abilities of terrestrial rodents.

Consequences of lost endings: caudal autotomy as a lens for focusing attention on tail function during locomotion.

Autotomy has evolved in many animal lineages as a means of predator escape, and involves the voluntary shedding of body parts. In vertebrates, caudal autotomy (or tail shedding) is the most common form, and it is particularly widespread in lizards. Here, we develop a framework for thinking about how tail loss can have fitness consequences, particularly through its impacts on locomotion. Caudal autotomy is fundamentally an alteration of morphology that affects an animal's mass and mass distribution. These morphological changes affect balance and stability, along with the performance of a range of locomotor activities, from running and climbing to jumping and swimming. These locomotor effects can impact on activities critical for survival and reproduction, including escaping predators, capturing prey and acquiring mates. In this Commentary, we first review work illustrating the (mostly) negative effects of tail loss on locomotor performance, and highlight what these consequences reveal about tail function during locomotion. We also identify important areas of future study, including the exploration of new behaviors (e.g. prey capture), increased use of biomechanical measurements and the incorporation of more field-based studies to continue to build our understanding of the tail, an ancestral and nearly ubiquitous feature of the vertebrate body plan.

Stochastic rules for predator and prey hunting and escape behavior in a lattice-based model

Understanding of ecosystem resilience and stability requires comprehending predator–prey dynamics because ecosystems consist of dynamically interacting subsystems that include predator–prey relationships. This relationship is closely related to the hunting–escaping strategies employed by the predator and prey. Therefore, understanding the effects of hunting and escaping strategies on ecosystems will lead to a better understanding of these systems. As an approach for describing the predator–prey interaction, lattice-based models have been adopted because this approach has strong advantages for simulating various dynamical processes of individual–individual interaction. In the models, each lattice cell is either considered as an attractive/repulsive cell, or an individual cell, or else it is empty. The attractive (or repulsive cell) can be interpreted as the prey (or predator) of the individual. These states allow us to incorporate the ecological processes of local antagonistic interactions, namely the spread of disturbances (by the predator) and regrowth or recovery (by the prey). These processes are directly related to the strategic behavior of individuals, such as hunting and escaping. In this study, we suggest a simple and effective mapping formula as a stochastic rule to describe the hunting and escaping behavior. This formula could be widely used not only in the behavior but also in competitive and cooperative relationships.

Diving in head first: trade-offs between phenotypic traits and sand-diving predator escape strategy inMerolesdesert lizards

Diving in head first: trade-offs between phenotypic traits and sand-diving predator escape strategy in<i>Meroles</i>desert lizards

Discovery of a specialised anatomical structure in some physoclistous carangid fishes which permits rapid ascent without barotrauma

Physoclistous fish are unable to rapidly ascend through the water column without significant risk of barotrauma via swim bladder hyperextension or rupture. Here, we report on the discovery of a highly specialised anatomical structure which permits some physoclistous fish species, the samson fish Seriola hippos and silver trevally Pseudocaranx georgianus, to vent swim bladder gas during ascent. Dissections of injected casts and X-ray imaging revealed the swim bladder ‘vent’ to consist of a membranous opening in the roof of the swim bladder which led to a flattened tube that bifurcated around the vertebral column and exited via a small, oval-shaped hole in the pharyngo-cleithral membrane underneath each operculum. Identification of these distinctive holes revealed that venting had occurred on ascent in 96 % of in S. hippos captured from depth. Decompression from simulated 30 m water depth in an experimental hyperbaric chamber revealed that venting in P. georgianus commenced when predicted swim bladder volume was approximately double that of its initial volume and ceased when the fish were again near neutrally buoyant. A homologous structure was identified in S. lalandi and S. dumerili. This structure represents an important step in the evolution of the teleost swim bladder which circumvents the normal physoclistous restriction on rapid ascents by eliminating, or minimising, barotrauma. Ecological benefits of this ability include an improved ability to capture prey, escape predators and perform ‘spawning rushes’. The increased resilience to barotrauma provided by the swim bladder ‘vent’ may also reduce the levels of post-release discard mortality for deep-water species which possess the structure.

Coexisting living stromatolites and infaunal metazoans.

Microbialites, bioaccretionary structures formed during the growth and metabolism of microorganisms (principally cyanobacteria) were the dominant lifeform in shallow late-Archean and Proterozoic oceans. During the Cambrian radiation of metazoan life, which began ~540 Mya, microbialite abundance and diversity further declined following a peak in the Mesoproterozoic. Notwithstanding contention, grazing and bioturbation effects of metazoans have been hypothesized as the dominant driver of modern microbialite scarcity. However, this metazoan-microbialite exclusion has not been fully explored in the few extant microbialites. Here we provide further evidence showing that living marine layered microbialites (stromatolites) coexist with a persistent assemblage of benthic macro-invertebrates, as has previously been demonstrated in some thrombolitic (clotted) microbialites. Surprisingly, these metazoans have active habits, such as burrowing, which should be expected to disrupt the layered matrix. As other studies have shown, through a network of burrows, metazoans can exploit local diurnal oxygen refugia within microbialites as well as escape predation. Our results, therefore, add novel evidence in support of the hypotheses that geologically, metazoans are not always incompatible with stromatolites, while ecologically, microbialites may act as micro-refugia for modern metazoans and historically have performed a similar inferred role in past ecosystems.

Ependymal Cells are a Heterogeneous Population in the Spinal Cord of the Leopard Gecko

The leopard gecko (Eublepharis macularius) is an emerging model for the study of spinal cord regeneration. As for many lizards, leopard geckos are able to self‐detach their tails (to escape predation) and then spontaneously regenerate a replacement. The regenerate tail is characterized by a centrally positioned spinal cord with a relatively simple morphology: a layer of ependymal cells surrounded by nerve tracts. We hypothesize that ependymal cells in the spinal cord are a heterogenous population. Prior to injury, virtually all ependymal cells of the original (uninjured) spinal cord express the neural stem/progenitor cell (NSPC) marker Sox2, and a subset of these cells also express the astrocyte marker glial fibrillary acid protein (GFAP). Neurons of the grey matter, but not ependymal cells, co‐express the neuronal markers HuCD and NeuN. During regeneration, ependymal cells remain Sox2+ and begin to express additional NSPC markers including Musashi‐1, βIII‐Tubulin and Sox9. Interestingly, a subset of ependymal cells in both the original tail stump and the newly formed regenerate spinal cord begin expressing HuCD, a protein otherwise characteristic of neuronal differentiation. These cells are negative for NeuN (a marker of neuronal nuclei) and are positionally restricted to locations bordering the central canal. A second subset of ependymal cells within the regenerating spinal cord begin to express GFAP and Vimentin but not HuCD. Our results suggest that there are at least three distinct populations of ependymal cells present during regeneration. The majority of ependymal cells are HuCD/GFAP− and display a dynamic NSPC profile following injury (Musashi‐1+/ βIII‐Tubulin+/ Sox9+). Two other populations are less widespread. HuCD+/GFAP−/NeuN− cells may represent a population of neuronal‐like central canal contacting cells, while HuCD−/GFAP+/Vimentin+ cells appear to be ependymo‐radial glia. This complex assemblage of cells may explain the remarkable regenerative abilities of the spinal cord in this species.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada, Discovery Grant (400358)

The effects of multiple obstacles on the locomotor behavior and performance of a terrestrial lizard.

Negotiation of variable terrain is important for many small terrestrial vertebrates. Variation in the running surface resulting from obstacles (woody debris, vegetation, rocks) can alter escape paths and running performance. The ability to navigate obstacles likely influences survivorship through predator evasion success and other key ecological tasks (finding mates, acquiring food). Earlier work established that running posture and sprint performance are altered when organisms face an obstacle, and yet studies involving multiple obstacles are limited. Indeed, some habitats are cluttered with obstacles, whereas others are not. For many species, obstacle density may be important in predator escape and/or colonization potential by conspecifics. This study examines how multiple obstacles influence running behavior and locomotor posture in lizards. We predict that an increasing number of obstacles will increase the frequency of pausing and decrease sprint velocity. Furthermore, bipedal running over multiple obstacles is predicted to maintain greater mean sprint velocity compared with quadrupedal running, thereby revealing a potential advantage of bipedalism. Lizards were filmed running through a racetrack with zero, one or two obstacles. Bipedal running posture over one obstacle was significantly faster than quadrupedal posture. Bipedal running trials contained fewer total strides than quadrupedal ones. But on addition of a second obstacle, the number of bipedal strides decreased. Increasing obstacle number led to slower and more intermittent locomotion. Bipedalism provided clear advantages for one obstacle, but was not associated with further benefits for an additional obstacle. Hence, bipedalism helps mitigate obstacle negotiation, but not when numerous obstacles are encountered in succession.

Adaptive evolution in locomotor performance: How selective pressures and functional relationships produce diversity.

Despite the complexity of nature, most comparative studies of phenotypic evolution consider selective pressures in isolation. When competing pressures operate on the same system, it is commonly expected that trade-offs will occur that will limit the evolution of phenotypic diversity, however, it is possible that interactions among selective pressures may promote diversity instead. We explored the evolution of locomotor performance in lizards in relation to possible selective pressures using the Ornstein-Uhlenbeck process. Here, we show that a combination of selection based on foraging mode and predator escape is required to explain variation in performance phenotypes. Surprisingly, habitat use contributed little explanatory power. We find that it is possible to evolve very different abilities in performance which were previously thought to be tightly correlated, supporting a growing literature that explores the many-to-one mapping of morphological design. Although we generally find the expected trade-off between maximal exertion and speed, this relationship surprisingly disappears when species experience selection for both performance types. We conclude that functional integration need not limit adaptive potential, and that an integrative approach considering multiple major influences on a phenotype allows a more complete understanding of adaptation and the evolution of diversity.

Is one defence enough? Disentangling the relative importance of morphological and behavioural predator-induced defences

Many organisms show predator-induced behavioural and morphological phenotypic plasticity. These defence mechanisms are often expressed simultaneously. To estimate the relative importance of these two defences, we conducted a laboratory experiment using tadpoles of the common frog (Rana temporaria) as prey and Aeshna dragonfly larvae as predators. We first raised tadpoles in the presence and absence of caged predators to induce differences in defensive morphology, and then conducted free ranging predator trials in environments that were either with or without the presence of predation cues to induce differences in defensive behaviour. This 2 × 2 design allowed us to separate the effects of inducible morphology from inducible behaviour. Caged predators induced deeper bodies and tailfins and reduced activity levels in tadpoles. The time to first capture was shortest in tadpoles without morphological or behavioural defences. Tadpoles with a behavioural defence had a significantly longer time to first capture. Tadpoles with only antipredator morphology tended to have a longer time to first capture as compared to those without any induced defences. This treatment also had a higher number of injured tadpoles as compared to other treatments, suggesting that inducible morphology facilitates predator escape due to the ‘lure effect’. However, tadpoles with both behavioural and morphological defences did not have a longer time to first capture as compared to tadpoles with only morphological or behavioural induced defences. Our results suggest that both behavioural and morphological antipredator responses contribute to reduced capture efficiency by predators, but their simultaneous expression did not have any additive effect to the time of first capture and survival, and that the morphology response is most effective when tadpoles are active.

Body size, swimming speed, or thermal sensitivity? Predator-imposed selection on amphibian larvae.

BackgroundMany animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals.ResultsNonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance.ConclusionsIn the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator–prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator–prey interactions and food web dynamics.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0522-y) contains supplementary material, which is available to authorized users.

Developmental exposure to organophosphate flame retardants causes behavioral effects in larval and adult zebrafish

BackgroundOrganophosphate flame retardants (OPFRs) have grown in usage since concerns about the health effects of the previously used polybrominated flame retardants led to their being phased out. The potential for OPFRs to cause adverse health effects of their own is still unexamined. Because of their structural similarities to organophosphate pesticides, which have themselves been heavily researched and shown to be neurobehavioral teratogens, we investigated the possibility that developmental exposure to two OPFRs, triphenyl phosphate (TPHP), and tris(1,3-dichloroisopropyl)phosphate (TDCIPP) might lead to behavioral impairment across the lifespan, as has been observed with the organophosphate pesticide chlorpyrifos. MethodsZebrafish were exposed to 0.03 or 0.3μM of TPHP, TDCIPP, or chlorpyrifos from 0 to 5days post fertilization. Vehicle control consisted of 0.03% solution of DMSO. At 6days post fertilization, larvae were tested on a locomotor assay. Separate cohorts of 6day old larvae that were not tested on the larval assay were allowed to grow to adulthood. At 12weeks post fertilization, these adult zebrafish were tested on a battery of behavioral assays that included tests of novel environment exploration, startle habituation, social affiliation, and predator escape. ResultsDevelopmental exposure altered zebrafish behavior across the lifespan. Larval zebrafish exposed to the 0.03μM doses of chlorpyrifos or TDCIPP exhibited significant (p<0.05) hyperactivity in the locomotor assay. Organophosphate exposure significantly (p<0.05) altered the time course of adult zebrafish behavior in the novel environment, startle habituation, and social affiliation assays. Predator escape behavior was significantly (p<0.05) reduced in fish exposed to the 0.3μM dose of TDCIPP. Exposure also caused hyperactivity in adult fish, with fish exposed to the 0.3μM dose of TDCIPP exhibiting significantly (p<0.05) elevated locomotor behavior in the novel environment assay. DiscussionEarly developmental exposure to OPFRs produced behavioral impairment that persisted into adulthood. These findings support broader research investigating the role of organophosphate compounds, including the OPFRs used here, in developmental neurotoxicity.

Impact of cercal air currents on singing motor pattern generation in the cricket (Gryllus bimaculatus DeGeer).

The cercal system of crickets detects low-frequency air currents produced by approaching predators and self-generated air currents during singing, which may provide sensory feedback to the singing motor network. We analyzed the effect of cercal stimulation on singing motor pattern generation to reveal the response of a singing interneuron to predator-like signals and to elucidate the possible role of self-generated air currents during singing. In fictive singing males, we recorded an interneuron of the singing network while applying air currents to the cerci; additionally, we analyzed the effect of abolishing the cercal system in freely singing males. In fictively singing crickets, the effect of short air stimuli is either to terminate prematurely or to lengthen the interchirp interval, depending on their phase in the chirp cycle. Within our stimulation paradigm, air stimuli of different velocities and durations always elicited an inhibitory postsynaptic potential in the singing interneuron. Current injection in the singing interneuron elicited singing motor activity, even during the air current-evoked inhibitory input from the cercal pathway. The disruptive effects of air stimuli on the fictive singing pattern and the inhibitory response of the singing interneuron point toward the cercal system being involved in initiating avoidance responses in singing crickets, according to the established role of cerci in a predator escape pathway. After abolishing the activity of the cercal system, the timing of natural singing activity was not significantly altered. Our study provides no evidence that self-generated cercal sensory activity has a feedback function for singing motor pattern generation.

Frequency-dependent flight activity in the colour polymorphic wood tiger moth

Abstract Predators efficiently learn to avoid one type of warning signal rather than several, making colour polymorphisms unexpected. Aposematic wood tiger moth males Parasemia plantaginis have either white or yellow hindwing coloration across Europe. Previous studies indicate that yellow males are better defended from predators, while white males have a positively frequency-dependent mating advantage. However, the potential frequency-dependent behavioural differences in flight between the morphs, as well as the role of male-male interactions in inducing flying activity, have not been previously considered. We ran an outdoor cage experiment where proportions of both male morphs were manipulated to test whether flying activity was frequencydependent and differed between morphs. The white morph was significantly more active than the yellow one across all treatments, and sustained activity for longer. Overall activity for both morphs was considerably lower in the yellow-biased environment, suggesting that higher proportions of yellow males in a population may lead to overall reduced flying activity. The activity of the yellow morph also followed a steeper, narrower curve than that of the white morph during peak female calling activity. We suggest that white males, with their presumably less costly defences, have more resources to invest in flight for predator escape and finding mates. Yellow males, which are better protected but less sexually selected, may instead compensate their lower flight activity by ‘flying smart’ during the peak female-calling periods. Thus, both morphs may be able to behaviourally balance the trade-off between warning signal selection and sexual selection. Our results emphasize the greater need to investigate animal behaviour and colour polymorphisms in natural or semi-natural environments.

Neurotoxicity of FireMaster 550® in zebrafish (Danio rerio): Chronic developmental and acute adolescent exposures

BackgroundFireMaster® 550 (FM 550) is the second most commonly used flame retardant (FR) product in consumer goods and has been detected in household dust samples. However, neurobehavioral effects associated with exposure have not been characterized in detail. We investigated the behavioral effects of FM 550 in zebrafish to facilitate the integration of the cellular and molecular effects of FM 550 with its behavioral consequences. The effects of developmental FM 550 exposure on zebrafish larvae swimming shortly after the end of exposure as well as the persisting effects of this exposure on adolescent behavior were studied. In addition, the acute effects of FM 550 on behavior with exposure during adolescence in zebrafish were studied. MethodsDevelopmental exposure to 0, 0.01, 0.1 or 1mg/L of FM 550 via immersion spanned 0–5days post fertilization, with larval testing on day 6 and adolescent testing on days 40–45. Acute adolescent (45dpf) exposure was to 0, 1.0 or 3.0mg/L of FM 550 via immersion, for 24h, with testing 2h or 1week later. The vehicle condition was colony tank water with .0004% (developmental) or .0012% (adolescent) DMSO. Zebrafish behavior was characterized across several domains including learning, social affiliation, sensorimotor function, predator escape, and novel environment exploration. ResultsPersisting effects of developmental FM 550 exposure included a significant (p<0.01) reduction in social behavior among all dose groups. Acute FM 550 exposure during adolescence caused hypoactivity and reduced social behavior (p's<0.05) when the fish were tested 2h after exposure. These effects were attenuated at the 1week post exposure testing point DiscussionTaken together, these data indicate that FM 550 may cause persisting neurobehavioral alterations to social behavior in the absence of perturbations along other behavioral domains and that developmental exposure is more costly to the organism than acute adolescent exposure.

Chronic exposure to environmentally-relevant concentrations of fluoxetine (Prozac) decreases survival, increases abnormal behaviors, and delays predator escape responses in guppies

This study evaluates the impact of fluoxetine, an antidepressant drug and common pollutant in aquatic environments, on growth, survival, and behavior in juvenile guppies and on predator escape responses in adult guppies (Poecilia reticulata). In juveniles, the effects of acute (4d) and chronic (35d) exposure on growth and survival were examined, and behavioral changes were noted throughout the chronic experiment. In adults, escape responses to a mock predator during chronic (28d) fluoxetine exposure were videotaped to determine the overall speed of response in treated vs. control fish. The effects of fish gender and the presence of a group/school on escape responses were also determined. Our results show that acute exposure to nominal concentrations of 0.03 and 0.5μg/L, levels within the environment, did not adversely impact juvenile guppy survival. However, chronic exposure significantly reduced weight, length, and belly width/girth measurements compared to controls. Chronic exposure also resulted in abnormal swimming behavior and reduced survival in juveniles. In adults, fluoxetine exposure significantly delayed predator escape responses in both males and females. Escape responses were also reduced when adults were tested either individually or in a group, with significantly more delayed responses seen in individually tested fish. Taken together, these findings suggest that fluoxetine can impact guppy populations, during both juvenile and adult stages, with chronic exposure resulting in decreased survival and growth and altered behavioral responses.

Regenerating tail muscles in lizard contain Fast but not Slow Myosin indicating that most myofibers belong to the fast twitch type for rapid contraction.

During tail regeneration in lizards a large mass of muscle tissue is formed in form of segmental myomeres of similar size located under the dermis of the new tail. These muscles accumulate glycogen and a fast form of myosin typical for twitch myofibers as it is shown by light and ultrastructural immunocytochemistry using an antibody directed against a Fast Myosin Heavy Chain. High resolution immunogold labeling shows that an intense labeling for fast myosin is localized over the thick filaments of the numerous myofibrils in about 70% of the regenerated myofibers while the labeling becomes less intense in the remaining muscle fibers. The present observations indicate that at least two subtypes of Fast Myosin containing muscle fibers are regenerated, the prevalent type was of the fast twitch containing few mitochondria, sparse glycogen, numerous smooth endoplasmic reticulum vesicles. The second, and less frequent type was a Fast-Oxidative-Glycolitic twitch fiber containing more mitochondria, a denser cytoplasm and myofibrils. Since their initial differentiation, myoblasts, myotubes and especially the regenerated myofibers do not accumulate any immuno-detectable Slow Myosin Heavy Chain. The study indicates that most of the segmental muscles of the regenerated tail serve for the limited bending of the tail during locomotion and trashing after amputation of the regenerated tail, a phenomenon that facilitates predator escape.